Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron.Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed.It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix.More oxidized matrix is observed in gray cast iron due to its large specific surface area.The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer.By contrast,the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers.It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.

Effect of Hot Deformation on Formation and Growth of Thermal Fatigue Crackin Chromium Wear Resistant Cast Iron

The formation and growth of thermal fatigue crack in chromium wear resistant cast iron was investigated, and the effect of hot deformation on the crack was analyzed by means of optical microscope and scanning electron microscope and high frequency induction thermal fatigue tester. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, hot deformation can improve the eutectic carbiders morphology and distribution, inhibit the generation and propagation of thermal fatigue cracks. In the experiment, the propagation rate of thermal fatigue crack reduces with the quantity of hot deformation increasing, which was analyzed in the point view of the activation energy of crack propagation.

Study on the Thermal Fatigue Behavior of Hot Deformed Wear Resistance Cast Iron and Effect of Carbide

The thermal fatigue behavior of wear resistance cast iron with different quantity of deformation has been investigated. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, approving that the more serious, the carbide breaks. The higher thermal fatigue resistance of wear resistance cast iron will be and thermal fatigue fracture belongs mainly to brittleness.

Niobium addition effect in molds at last cooling step on EN-GJL250 gray cast iron: Microstructural changes and electrochemical behavior

The purpose of this study was to determine the impact of niobium addition as an inoculation element on the microstructure and electrochemical properties of EN-FGL250 gray cast iron. Niobium additions are in a powder form and have a 0.5 mm particle size at dfferent proportions of 1 wt.% and 3 wt.%. The addition was done during casting of the metal in the mold at the last cooling step of the melt cast iron. These additions have a significant impact on the phenomenon of solidifi cation as the metal powder deposited in the sand molds creates new centers of germination and absorbs a lot of heat. The cooling rate directly affects the microstructure and electrochemical behavior. This is confirmed by SEM observations and electrochemical tests. Furthermore, the addition of niobium transforms the microstructure of gray cast iron from cellular structure into totally dendritic structure. As a consequence, the niobium addition affected the shape and size of graphite, thus considerably reducing the corrosion current density by increasing the polarization resistance Rp.

Monitoring of Quality of Vermicular Cast Iron from the Front of the Furnace

Vermicular cast iron is used in certain fields because of its special physical properties. However, it is difficult to control the quality from the front of the furnace owing to the narrow range of vermiculizer and other elements that can be added to the iron. A real time method was developed to monitor the vermicular- graphite ratio of the cast iron based on fast measurements of the melt surface tension. The system includes a detector and a control unit that measure the amplitude and frequency of bubbles rising in the melt. This paper describes the methodology for measuring the surface tension of the melt and test results monitoring the vermicular-graphite ratio of the vermicular cast iron from the front of the furnace. The relationship between surface tension and graphite shape has been established. The results show that this system can quickly evaluate the vermicular-graphite ratio of the cast iron.

蠕墨铸铁V型缸体铸造工艺开发与试制

基于V型缸体产品结构和铸造工艺的复杂性,采取包型立浇工艺方案,通过CAE模拟分析及进一步优化,采用3D打印砂型、整体组芯的造型工艺,样件试制一次成功,产品质量满足技术要求,为该产品量产工艺、正式工装的开发提供参考。

《压缩天然气发动机用耐热疲劳铁素体蠕墨铸铁件》团体标准解读

《压缩天然气发动机用耐热疲劳铁素体蠕墨铸铁件》T/CFA020101071-2022标准是我国首次制定的推荐性团体标准。介绍了该标准起草的主要过程,对该标准的适用范围、引用文件、材料牌号、技术要求、生产方法、试验方法、检验规则与判定以及标识、参考化学成分、热疲劳耐久试验要求进行了探讨,以便于该标准的推广应用。

Sn对蠕墨铸铁组织与抗热疲劳性能的影响

研究了Sn含量对汽车制动鼓用蠕墨铸铁中蠕墨数量、形态、基体组织以及抗热疲劳性能的影响规律。结果表明，Sn可以明显改变蠕铁中的珠光体含量，对蠕化率无明显影响，可以改变蠕铁热疲劳性能。Sn含量为0．06％（质量分数，下同）时，珠光体含量最高为95％，片层间距为0．07μm。Sn含量增加时，石墨轴比率逐渐上升，石墨变得细长且分叉增多。在20～600℃循环条件下，含0．06％Sn时蠕铁的热疲劳裂纹长度最短，抗热疲劳性能最好。

石墨形态对铸铁热疲劳性能影响的研究

采用板状带V型缺口的HT200、RuT340和QT600试样,通过对试样进行反复加热、冷却的方法,研究了石墨形态对铸铁热疲劳性能的影响,为金属锭模的合理选材提供依据。试验结果表明,在热循环过程中,微裂纹总是起源于石墨相;微裂纹产生后,主裂纹通常是沿着石墨和石墨间最近的基体扩展;在20-650℃间的热循环条件下,球墨铸铁的抗热疲劳性能最好,蠕墨铸铁次之,灰铸铁最差。

一种包内快速预测铁水石墨形态的新方法及新装置

提出一种包内快速预测铁水石墨形态的新方法及新装置．新方法的核心是以气泡幅频参数所形成的当量张力来表征铁水石墨形态，故称幅频当量法．应用该方法可在１０ｓ 内完成全部测试过程．以气泡幅频当量法为基础而研制的微机化测试新装置主要由快换探头、微型气路系统、高精度单片机数据采集系统等组成，具有操作简便。

炉前快速评价球墨铸铁球化质量的新方法

介绍一种球铁球化质量炉前快速检测新技术。在理论分析与实验研究的基础上 ,提出了一种快速测定液态合金表面张力的新方法——气泡幅频当量法。通过毛细管向被测液体吹气 ,利用高精度数据采集与处理系统快速测得规定时间内所形成气泡的个数 (频 )以及气泡内微压差变化 (幅 ) ,以此两参数作变量 ,经适当运算后形成的当量来表征液体表面张力的变化。铁水表面张力与其石墨形态之间有密切关系 ,因此 ,应用气泡幅频当量法 ,可以实现球铁球化质量的炉前快速检测。

改性纳米SiC粉体强化球墨铸铁的耐磨损性能

采用改性纳米SiC粉体对球墨铸铁进行了强韧化处理,研究了不同的纳米SiC粉体加入量对球墨铸铁的微观组织、力学性能以及耐磨损性能的影响。结果表明,经改性纳米SiC粉体强韧化处理后,球墨铸铁中的石墨球尺寸减小,圆整度提高,铁素体含量增多,球墨铸铁的韧性和耐磨损性能提高。当粉体加入量为0.1%(质量分数)时,其延伸率和冲击功分别增加了19%和194%。耐磨损性能提高的原因是石墨球形态的改善和基体组织韧性的提高。

球铁铝锭模材料热疲劳性能的研究

模拟铝锭模的使用条件,研究了不同基体组织球墨铸铁的热疲劳性能。结果表明,退火铁素体铝铸锭模使用寿命最长。该铝锭模安装在包头铝业公司的2台铝锭连续铸造机上使用,平均每天铸锭48t／台,连续使用410天。而普通材质的球铁铝锭模使用寿命仅为120到150天左右。

石墨形态及合金元素对铸铁抗热疲劳性能的影响

对石墨形态、合金元素等对铸铁抗热疲劳性能的影响进行了研究。加入提高抗氧化性的合金元素可显著提高铸铁的抗热疲劳性能。从首次产生裂纹的循环次数、裂纹扩展速度及变形量等综合考虑，蠕铁的抗热疲劳性能最好。

石墨形态对铸铁热疲劳性能的影响

主要研究了石墨形态对铸铁热疲劳性能的影响,为高速列车制动盘的合理选材提供依据。试验结果表明:蠕墨铸铁的耐热疲劳性能最好,球墨铸铁次之,灰铸铁最差。

蠕墨铸铁铁道车辆闸瓦摩擦磨损性能研究

随着铁路车辆向高速和重载方向发展，人们开展了抗热疲劳剥落能力优异的蠕墨铸铁在火车刹车闸盘上的应用研究。然而研究内容只涉及其耐磨性，在摩擦性能方面还很少有研究成果公开发表。因此，以含磷蠕墨铸铁为研究对象，系统地考察了石墨形态和磷含量变化对材料摩擦磨损性能的影响，并且依据研究结果制造火车闸瓦进行了实际装车使用性能的试验研究。结果表明，在给定的试验条件下于几种不同形态石墨的铸铁中，蠕墨铸铁既有优良的耐磨性，又有高的摩擦系数，故其是适合制造铁道车辆闸瓦的材料之一；随着磷含量的提高，蠕墨铸铁的摩擦系数快速增大，而磨损量则明显减小，而且蠕墨铸铁闸瓦的制动火花性能也明显改善；在同车对比运行试验以后，含磷蠕墨铸铁闸瓦摩擦表面的裂纹数量和尺寸都远比高磷灰铸铁闸瓦摩擦表面的小，而与中磷灰铸铁闸瓦摩擦表面的相当，可见使用含磷蠕墨铸铁闸瓦能够保证车辆安全运行。

高碳当量薄壁灰铸铁纺机铸件的孕育处理

采用Ba、Ca、Si、稀土、石墨、Al为主要成分的复合孕育剂对高碳当量 (CE =4.3 %～ 4.4%)薄壁灰铸铁件进行孕育处理 ,研究了复合孕育处理对薄壁铸件的白口倾向、石墨形态及力学性能的影响。结果表明 ,与常用的FeSi75孕育剂相比 ,复合孕育剂对降低薄壁铸件的白口倾向、改善石墨形态及力学性能等方面均具有显著效果。当复合孕育剂的加入量w为 0 .3 5 %时效果最佳 ,消除了薄壁灰铸件的白口现象 ,且薄壁和厚壁部分的A型石墨形态均匀、细小 ,抗拉强度提高近 10 %。

微合金梯度石墨铸铁玻璃模具材料研究

本文通过控制铸铁生产中的合金元素量、浇注温度、孕育剂量,得到在模具壁厚方向形成三级梯度石墨灰铸铁。利用SEM观察金相试样评价石墨形态、尺寸、分布;测试试样各梯度石墨区域的布氏硬度值评价铸铁的力学性能;观察热疲劳试样的疲劳裂纹的扩展评价试样的热力学性能。试验结果发现合金元素量V：0.11%~0.15%、Ti：0.15%~0.21%、浇注温度1360~1320℃、孕育剂量在0.35%~0.50%,模具在内腔区形成细小D型石墨,模具腔壁石墨逐渐长大B型,最后形成A型石墨的三级梯度石墨结构;梯度石墨结构兼顾内腔区模腔表面质量良好、径向高效散热能力和优异的耐热疲劳性能。

制动鼓用加锡蠕墨铸铁抗热疲劳性能的研究

通过在铸铁中添加不同含量的Sn,分析Sn含量变化对铸铁在600~20℃交变温度下抗热疲劳性能的影响规律。结果表明,当Sn的添加量为0.06%时,在270℃等温淬火0.5 h后,铸铁的基体组织为奥铁体,具有最佳的抗热疲劳性能。